We all have moments of narcissism now and again--times when we hold our own needs above those of other people. Narcissistic personality disorder is a far more pervasive and destructive condition: a distorted sense of self-importance fed by the active exploitation of other people. As a clinically defined personality disorder, narcissism causes considerable problems in the patient's home and personal life, leading him unable to function as an adult over the long term. Though clinical narcissists can be extremely charming and persuasive when they need to be, their condition prevents them from achieving any stability in their lives.

Grandiosity

The essence of narcissistic personality disorder is an overpowering sense of self-importance: a belief that the patient is inherently superior to other people. He exaggerates his accomplishments, invests his activities with profound meaning, and often evinces a haughty or arrogant attitude.

Interpersonal Exploitation

Accompanying that grandiosity is an inability to empathize with other people. Narcissists are often very charismatic and can make people around them feel special and desired. They do that in order to leverage what they want out of them: validation, respect, and favors they aren't entitled to. When people question this behavior or challenge the narcissist, he devalues them and casts them aside, only to soon find new "friends" to exploit. Narcissists have a very hard time empathizing with others or acknowledging their needs: they themselves are the only ones who really matter in their lives.

Disconnect From Reality

Narcissists tend to fantasize about their own achievements: being consumed with visions of extraordinary success or inhuman attractiveness. They speak of grand accomplishments which they haven't succeeded at yet, or brilliant work which they are constantly in the process of creating yet never find the time to finish. This fantasy life helps explain their proclivity for exploiting others: the more people they can convince of their own importance, the more that importance feels real, regardless of what the facts say. To that end, narcissists lie extremely readily, and have a knack for wrapping their lies in just enough truth to convince others of their veracity. Indeed, they often believe their own lies, which allows them to deliver their distortions with persuasive conviction.

Entitlement

As part of their self-importance, narcissists exhibit a distorted sense of entitlement, claiming numerous privileges which they haven't earned. They don't believe they need to wait their turn, bide their time or go through the channels that other people do. They may insist on having the best of everything and lose their tempers when they don't get it. Their work ethic often suffers under this delusion, since "special" people like them shouldn't need to apply themselves to accomplish their goals.

Fragility

The irony of the condition is that, for all their professed self-confidence, narcissists actually possess an extremely fragile self-esteem. Their grandiosity is an act to hide the belief (often sub-conscious) that they are small, weak, or chronic failures. They often envy other people's accomplishments and, in keeping with their grandiosity, believe that other people are envious of them. They're easily hurt and may lash out at people in inappropriate ways--ironic, considering how casually they hurt others. This fragility often leads them into a profound sense of denial: narcissists rarely acknowledge their condition, and as such remain extremely difficult to treat.